The Bi-Gaussian approach: A simple method for recovery estimation

A new and simple method is proposed to obtain estimates of recovery functions: the Bi-Gaussian approach. Existing methods estimate recovery functions with conditional distributions where the conditioning set is all the data available. Here instead the simple kriging estimate of the Gaussian transform is proposed to be used. Results in the point recovery case are identical to the multi-Gaussian approach of Verly (1983, 1984), whereas in the non-point-support situation, an approximation is derived which saves computer time as compared to employing the strict multi-Gaussian hypothesis. Two examples compare favorably with the well-established disjunctive kriging method (discrete Gaussian model).     

Collisionless Saturnian rings

We show that particles orbiting a central body ($\text{i.e.}$, Saturn's rings) can be assembled into one or more dense ($\text{i.e.}$, opaque) independent rings without interparticle collisions taking place despite the inevitable particle oscillations about the ring plane. The resultant apparent bulk motion is a slow “rolling” motion of the ring, as it orbits, the individual rings describing a “helical” motion. Such rings would only evolve due to external perturbations or (slow) internal gravitational perturbations, since the particles need never collide. This picture opens up the possibility of having hollow rings, for example. Moreover, it is possible that an initially uniform disk of randomly moving particles may spontaneously separate into a series of such rings. The consequence would be a striated disk having virtually zero internal viscosity.     

Primitive xenon in diogenites and plutonium-244-fission xenon ages of a diogenite,a howardite,and eucrites

Abstract The ²⁴⁴Pu-fission-¹³⁶Xe retention ages of howardites, eucrites, and diogenites (HEDs) show that these meteorites have retained Xe since they were formed about 4500 Ma ago. For the Garland diogenite and the Millbillillie eucrite, we obtain fission Xe ages of 4525 ± 40 Ma and 4486 ± 40 Ma, respectively. If Xe isotope data reported by other workers are also considered, we conclude that the monomict equilibrated eucrites Camel Donga, Juvinas, and Millbillillie formed about 40 Ma later than Pasamonte, a polymict unequilibrated eucrite. Stannern, a monomict equilibrated brecciated eucrite, yields a ²⁴⁴Pu-¹³⁶Xe age of 4442 Ma. The ⁴⁰K-⁴⁰Ar retention ages fall, for most HEDs, into the 1000–4000 Ma age range, indicating that ⁴⁰Ar is generally not well retained. The good retentivity for Xe of HEDs allows us to study primordial trapped Xe in these meteorites. Except for Shalka, in which other authors found Kr and Xe from terrestrial atmospheric contamination only, we present for the first time Kr and Xe isotopic data for diogenites. We studied Ellemeet, Garland, Ibbenbühren, Shalka, and Tatahouine. We show that Tatahouine contains two types of trapped Xe: a terrestrial contamination acquired by an irreversible adsorption process and released at pyrolysis temperatures up to 800 °C, and indigenous primordial Xe released primarily between 800 °C and 1200 °C. The isotopic composition of this primordial Xe is identical to that proposed earlier to be present in primitive achondrites and termed U-Xe or “primitive” Xe, but it has not been directly observed in achondrites until now. This type of primitive Xe is important for understanding the evolution of other Xe reservoirs in the Solar System. Terrestrial atmospheric Xe (corrected for fission Xe and radiogenic Xe from outgassing of the Earth) is related to it by a mass dependent fractionation favoring the heavier Xe isotopes. This primitive Xe is isotopically very similar to solar Xe except for ¹³⁴Xe and ¹³⁶Xe. Solar Xe appears to contain an enrichment of unknown origin for these isotopes relative to the primitive Xe.     

Rhythmic pelagic successions and terrestrial orbital variations. The example of the Lower Cretaceous from Angles (SE France)

An harmonic analysis of limestone bed and marl interbed thicknesses of pelagic Berriasian-Barremian interval from the Angles area (SE France) shows that marly parts of the succession contain frequencies significantly different from calcareous ones. Some of the resulting periods are in the Milankovitch frequency band but many others are different from those predicted by the orbital theory.     

Polyphase wrench tectonics in the southern french Massif Central: kinematic inferences from pre- and syntectonic granitoids

In the Variscan French Massif Central, the South Limousin area consists of low- to medium-grade metamorphic rocks intruded by two granitic bodies. The structural and textural analyses of these plutons undertaken in parallel with the structural analysis of their host rocks allow us to characterize and to date different stages in the tectonic evolution of this area. This study shows that the South Limousin area experienced successivelly two strike-slip events along two geographically distinct shear zones, from north to south the left-lateral Estivaux and the right-lateral South Limousin strike-slip faults, respectively. These ductile faults subdivide the South Limousin into three structural units, from north to south they are the Upper Gneiss unit, Thiviers-Payzac unit .and Génis unit. The two granitic bodies intrude the Thiviers-Payzac unit only. The younger Estivaux granite is a syntectonic pluton which emplaced during left-lateral wrenching. ⁴⁰Ar/³⁹Ar dates from biotites indicate an Early Carboniferous age (346 ± 3 Ma). The older granite is a pretectonic body. It is the Ordovician Saut du Saumon augen orthogneiss in which detailed structural analyses show the polyphase nature of the solid-state deformation. Our microtectonic data indicate that the right-lateral motions overprint the left-lateral ones and produce apparently symmetrical fabrics.     

Linked fluid and tectonic evolution in the High Himalaya mountains (Nepal)

Fluid inclusions were studied in a quartz lens from the structurally highest unit of the Himalaya mountains in Nepal from a textural, geometrical, chemical and isotopic point of view. Six types of fluid inclusions were distinguished. One of these types consists of annular inclusions; this shape is attributed to a confining pressure increase in a non-isotropic stress field. Two successive stress fields were deduced from the orientation of the inclusion planes relative to the schistosity. The bulk composition of the fluid was dominated by CO₂ (>84 mol%) and H₂O. The composition remained constant during the whole history of the sample indicating that it was buffered by the carbonaceous host rock and/or that one single fluid was reworked in situ by decrepitation. Stable isotope of fluids and minerals indicate (1) that fluids were buffered by surrounding rocks for O and C and (2) that at least two types of water (metamorphic and meteoric) were involved. Finally, a P-T-t-- path is proposed for the sample, taking into account the southward thrusting along the Main Central Thrust, the northward tectonic denudation of the Himalaya mountains inducing tectonic burying below the Annapurna Range, and lastly, rapid uplift.